1. Field of the Invention
The present invention relates to an ignition system for internal combustion engines installed mainly on automotive vehicles.
2. Description of the Prior Art
Ignition systems are known in the art in which in response to one of a plurality of ignition signals from an engine control unit each of a plurality of power transistors is turned on and off to switch on and off the primary current flow in an ignition coil. In one such ignition system (e.g., Journal of Nippondenso Technical Disclosure, Reference Number 37-063), the output operating state of each of a plurality of power transistors is detected to trigger a monostable multivibrator and the OR operation is performed on the outputs of the monostable multivibrators to apply an ignition monitor signal to the engine control unit.
However, the conventional ignition system of this type requires a monostable multivibrator for each power transistor and therefore there is the disadvantage of complicating the circuit construction and increasing the cost. Also, the monostable multivibrator generally uses a capacitor and the fabrication of such monostable multivibrators in a monolithic IC requires that their capacitors are externally connected to the bumps projected from the IC. Thus, this system is disadvantageous from the standpoint of reliability in that an increase in the number of monostable multivibrators increases the number of bumps on a monolithic IC and the number of capacitors.